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CAD model of a BD camalot number 1
Tom Sherman wrote:I think I learned something. Cam angle/ logarithmic spirals are a function between planar x/y and so keeping that function a constant, your working in the same game. By using a double-axle or effectively offsetting the axle CL, they are able to package the, call-it, x-gains of a larger value, but packaging it in to a smaller unit by offsetting. pretty simple, but really cool to understand. It's like a headstart. I don't understand the cam angle function enough to draw differences between Metolius and Black Diamond, but would be interesting to see. OK Kyle, now draw an X4 so I can learn that variable axle bullshit they got goin on there.The variable axle uses the exact same principle as the double axle of the C4. The only difference is that there isn't room to fit two axles in that small of a package so they just shift the center of the axle for two lobes relative to the center af the axle for the other two lobes by varying the axle's diameter. |
kennoyce wrote: The variable axle uses the exact same principle as the double axle of the C4. The only difference is that there isn't room to fit two axles in that small of a package so they just shift the center of the axle for two lobes relative to the center af the axle for the other two lobes by varying the axle's diameter.OH YEAH!!! No but how the @#$% does that work? If I tape a watermelon to a broomstick handle and twist it, Its gonna rotate around the center, not spin around it's own axis in proximity. Even if you alter the area that receives your axle, on the cam lobe, your messing with the intrinsic function of the spiral.... Going to do some more research into it. Looks like there was one good thread on this lingering in 2012, trying to get through it. |
Tom Sherman wrote: OH YEAH!!! No but how the @#$% does that work? If I tape a watermelon to a broomstick handle and twist it, Its gonna rotate around the center, not spin around it's own axis in proximity. Even if you alter the area that receives your axle, on the cam lobe, your messing with the intrinsic function of the spiral.... Going to do some more research into it. Looks like there was one good thread on this lingering in 2012, trying to get through it.Tom, I'm not sure i understand your question, but you don't have to alter the area that receives the axle because as you said, that would change the cam angle. Think about it this way, you stick the watermelon on the broomstick but make sure the broomstick isn't going through the center of the watermelon. You then secure the watermelon to the stem of the cam so that the broomstick and the center of the watermelon are both on a plane that is perpendicular to the stem. Now you just put the cam lobes onto the watermelon and the broomstick, you don't charge the center of the lograthmic spiral of the lobes, you just drill out the inner lobes so that they fit on the watermelon. |
kennoyce wrote: Tom, Think about it this way,Not sure if you want watermelon right now or are messing with me. I used the origin of the logarithmic spiral as the axis of rotation and assumed this to be some necessary thing. What you're proposing, you'd still be rotating around broomstick CL axis, but your watermelon cam would be rotating at some leg off of its' origin. If this is plausable, why do we even need the greater diameter offset axis, i.e. watermelon. Why can't we just rotate half the lobes off the single centerline, but at an extended leg. I think there is something more to this. I don't think it's so simple. Something in the receiving of the offset axle has to account for something... |
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Yup just check it, the cam has to rotate around its logarithmic origin, otherwise while you still maintain a constant cam angle, your angle of tangency is variable, which is no bueno |
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This is a great thread. Vaughne wrote:Nice job dude. That is some solid work!ha ha, very punny. |
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Kyle, this is pretty cool man. I'm an industrial designer by trade so I appreciate the cad work (and the nerdy desire to recreate and better understand a bitchin mechanism)... Anyone who is "missing the point" or wondering why he would take the time to do this.... I think a better question would be why you're taking the time to try and rain on his parade? haha It's impressive work and I'm pumped to have the IGES file! Creo here I come! |
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admittedly the thumb piece needs some work this was a quick model for me in my spare time. I would like to actually draw the logarithmic spiral on the next cam I CAD up. I have a nice set of X4s so I will do that one up next chance I get. @ Jovid I am also an Industrial Designer |
Tom Sherman wrote: Not sure if you want watermelon right now or are messing with me. I used the origin of the logarithmic spiral as the axis of rotation and assumed this to be some necessary thing. What you're proposing, you'd still be rotating around broomstick CL axis, but your watermelon cam would be rotating at some leg off of its' origin. If this is plausable, why do we even need the greater diameter offset axis, i.e. watermelon. Why can't we just rotate half the lobes off the single centerline, but at an extended leg. I think there is something more to this. I don't think it's so simple. Something in the receiving of the offset axle has to account for something...Sorry, I guess I took the watermelon analogy too far;) So, I'm trying to think of how to explain this better. The thing is, the axle is a single piece, so in my previous analogy, the watermelon and the broomstick are one piece, i.e. the watermelon is fixed to the broomstick so it can't rotate around it. This whole unit is then fixed to the cam's stem which also holds it in place and doesn't allow rotation. because the centerline of the wide portion of the axle (watermelon) is not aligned with the centerline of the skinny portion of the axle (broomstick), it is equivalent to having two separate axles. The cam lobes still rotate around the center of their respective logarithmic spirals, just the hole drilled through the center of the inner lobes logarithmic spiral has a larger diameter to fit over the larger portion of the axle than the outer lobes axle hole. If this still doesn't make sense I can throw a model together at work on Monday, but alas, I don't have any CAD software on my home computer. |
Tom Sherman wrote: Does double axle design not actually increas range per say.Unfortunate timing, as I had an article on this subject at theclimbinglab.com, but finally shuttered the site a couple days ago and deleted everything (hadn't touched it in years due to lack of time and the SQL backend went wonky). From memory, the dual axle will give a maximum theoretical range advantage of ~10%, assuming maximal distance between the axles. C4 Camalots are far from optimized in this regard (IMO likely due to sharing heads between sized), and the bulk of their greater range comes from the larger tangent angle of the log spiral. I probably still have the Mathematica program I wrote to prove this, but will instead suggest you poke at it yourself since it is a rather worthwhile/interesting problem to work through. Give a holler if you get stuck. |
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this is some pretty cool stuff. way too complicated for me to understand but its cool to think about. on the off chance that you actually end up designing some new cams, i would definitely be one of your first customers. i love seeing new designs, especially coming from an individual rather than a company, and even if it turns out to be crap its still cool to have a piece of climbing history. who knows, you could be the next greg lowe |
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Tom Sherman- Found my program, and yes, with all other things being equal the additional range given by a dual axle cam compared to a single axle cam is ~10%. For a 30.2mm wide crack using a 15 degree cam lobe I'm getting a theoretical maximum expansion ratio of 1.67 for single axle, and 1.74 for dual axle(assuming a minimum of 5mm of material around the axle). |
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Tom, double axle does increase range. What's the limit to how far you can retract? Until the tip of the spiral crosses the midline and is bumping up against the opposite wall. That happens later with double axle. |
Tom Sherman wrote:So was just playing around with this in CAD, I didn't download yours, but drew a logarythmic spiral and was screwing around. Initial thoughts. Does double axle design not actually increas range per say. (Range is inextricably linked to a function of cam angle) But rather double axle increases range relative to overall unit length (width whatever you call it). So that two untis of equal cam angle and equal size, the one with the double axle will have a greater expansion/ contraction whatever??? This is pretty cool stuff! Thanks for the morning buzz.EDIT: I din't realize there were two pages on this and Aric has it spot on. Continue reading if it may help you out/ visualize. Interesting though Aric that you don't think the distance is optimized for the BD Cams, because as I was looking at mine (#3 C4) it seemed spot on. That may just be the one though... I'll bite and nerd out for a bit. Your theory is totally sound, and I'll back you on that. Especially with that sketch you provided, it definitely helps validate it. Now I'm trying to understand your question (maybe rhetorical?), so you are asking if JUST having two axles over one axle will increase your range? (Assuming: Same logarithmic spiral, Same overall width of unit when lobes at rest) To break it down further than just the width of the unit. As you stated above, range may be a function of the width. However, with the assumptions made I don't believe the entire width of the unit, but the length of the lobe from axle to tip affects the range. To increase this length the second axle is introduced and then the distance between the axles becomes the constraint for range. Theoretically the axles should be spread apart as far as they can go, being constrained my numerous other factors then. So this is where your sketch isn't providing a completely accurate comparison. If you measure the length of the individual lobe from axle to tip as shown here: --- Invalid image id: 110102683 --- Then you get an increase in lobe length of about 0.5". This allows the second axle to be displaced 0.5" which then allows the lobes to come closer together at maximum rotation. Ergo, more range. Now having said all that and literally staring at a #3 C4 (By the way has 1" displacement between axles and 3 3/8" width, with 2 3/8" lobe lengths) in front of my face for half an hour...The distance between the axles is heavily constrained by the overall width of the cam unit. The optimal distance between the axles for each size cam out there definitely has probably been thought out several times over. So yeah...Maybe that answered your possible question? Maybe that just made life that much more confusing for everyone. Either way it helped me pass the time on a Friday night with a few brews. Thanks and Cheers, Mac |
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Definitely my favorite thread on here! As an ME with a little design experience, you guys rock! Awesome job on the model. My friend and I modeled up some Forged Friends because we wanted to try to make some (and then didn't have to deal with cables and such for the modern single stems) but cam angles and range has always been an interesting part of looking at them. Maybe we can look at making a dual axle forged friend! |
MacM wrote:Interesting though Aric that you don't think the distance is optimized for the BD Cams, because as I was looking at mine (#3 C4) it seemed spot on. That may just be the one though...Been ages since I looked and was going by memory. Looks like 3 and below are pretty good, 4 and above not so much. Pretty easy to see in this pic:  |
Tom Sherman wrote:And i've got access to CNC.... profit??? Why is the stem trigger twisted off axis?Will you make me a coffee mug shaped like a #11 hex? You won't make much money but at least I'll have a #11 hex shaped coffee mug. I'm somewhat serious. |
nicelegs wrote: Will you make me a coffee mug shaped like a #11 hex? You won't make much money but at least I'll have a #11 hex shaped coffee mug. I'm somewhat serious.Dead serious! Please make mine anodized with a locking oval biner handle! |
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I've got access to a waterjet cutter. I could churn out crude looking cam lobes all day for the cost of material and about $1/min of nozzle wear. I'm thinking of maybe making some bigguns... |
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I'd be down for a #11 Hex Coffee cup as well! Also a "crude" #4 C4 Lobe to attach as a handle. Anybody know how to use Kickstarter in here?! I hear this is what all the kids are doing these days. |
